Ultrafast Poly(disulfide) Synthesis in the Presence of Organocatalysts

Abstract

An organocatalyst-mediated, extremely rapid, robust, and practical poly(disulfide) synthesis method is introduced to polymer chemistry. A variety of organocatalysts were initially screened using commercially available 1,6-hexanedithiol and diisopropyl azodicarboxylate (DIAD) to reveal the best catalyst for the process. Remarkably, although a very low amount of catalyst loading (5%), all the catalysts examined afforded poly(disulfide) in 1 min with low to high molecular weights. Among them, triphenylphosphine was selected as the suitable catalyst after the kinetic measurements and used to determine the optimum conditions for polymerization. Various poly(disulfide)s with molecular weights up to 85.6 kDa could be successfully prepared using optimum conditions. Poly(disulfide) synthesis was also attempted with a “catalyst-free” approach, it was found that a polymer can be prepared under this condition, and its molecular weight increases with increasing temperature. The obtained polymers were characterized using common spectroscopic measurements, and the results revealed that the hydrazine unit derived from DIAD was incorporated into polymer chains as an end-capping agent. Also, a depolymerization study was achieved on a model poly(disulfide) using dithiothreitol as a reducing agent. It is believed the straightforward poly(disulfide) synthesis method comprising mild conditions introduced in this study will be of great interest in synthetic polymer chemistry.